The present invention relates generally to a metal line of a semiconductor device and a method for forming the same, and more particularly, to a metal line of a semiconductor device which can improve the characteristics of a diffusion barrier, thereby improving the characteristics and the reliability of a semiconductor device, and a method for forming the same.
Generally, in a semiconductor device, metal lines are formed to electrically connect elements or lines with each other. Contact plugs are formed to connect metal lines formed on different layers with each other, for example lower metal lines and upper metal lines. A current design trend is high integration of a semiconductor device, as a design rule decreases to conform to the high integration trend, the aspect ratio of a contact hole in which a contact plug is to be formed gradually increases. As a result, the difficulty and the importance of a process for forming the metal line and the contact plug have been noted.
Primarily, aluminum and tungsten are used as a material for the metal line of a semiconductor device since aluminum and tungsten have good electrical conductivity. Recently, research has been conducted for using copper as a next-generation material for a metal line because copper has excellent electrical conductivity and low resistance when compared to aluminum and tungsten. Copper (Cu) can therefore solve the problems associated with resistance-capacitance (RC) signal delay in the semiconductor device having a high level of integration and high operating speed.
When utilizing copper as the material for a metal line, unlike the case of using aluminum, the copper can diffuse to a semiconductor substrate through an insulation layer. The diffused copper acts as a deep-level impurity in the semiconductor substrate and induces a leakage current. Therefore, a diffusion barrier must be formed at an interface between a metal line of copper and the insulation layer. Generally, the diffusion barrier is made of TaN/Ta layers.
Hereinbelow, a conventional method for forming a metal line of a semiconductor device will be briefly described.
First, an insulation layer is formed on a semiconductor substrate so as to define a metal line forming region. Then, TaN/Ta layers serving as a diffusion barrier and a copper seed layer are sequentially formed on the surface of the insulation layer. Next, after forming a copper layer on the copper seed layer, a metal line is formed by removing the copper layer and the copper seed layer through a CMP (chemical mechanical polishing) process until the insulation layer is exposed.
However, in the conventional art described above, as the size of cells decreases, the thickness of the diffusion barrier also decreases. As a result, properly preventing the diffusion of a copper constituent by means of the diffusion barrier formed according to the conventional art is difficult.
Also, in the conventional art described above, increasing the thickness of the diffusion barrier to improve the characteristics of the diffusion barrier is also difficult due to the high integration trend. Due to this fact, as the characteristics of the diffusion barrier deteriorate, the characteristics and the reliability of a semiconductor device also deteriorate.